🐛 FIX: render hardbreak and inline HTML in image alt text

[chuenchen309]

RendererHTML.renderInlineAsText builds the alt attribute for images by walking the inline token stream, but it only handles text, image and softbreak tokens. hardbreak, html_inline and html_block are silently dropped, so a hard line break or inline HTML inside an image description disappears from the alt text.

from markdown_it import MarkdownIt
md = MarkdownIt("commonmark")

md.render("![foo\\\nbar](/url)")   # hard break (backslash)
# now:  <p><img src="/url" alt="foobar" /></p>
# want: <p><img src="/url" alt="foo\nbar" /></p>   (soft break already does this)

md.render("![a<b>c](/url)")        # inline HTML
# now:  <p><img src="/url" alt="ac" /></p>
# want: <p><img src="/url" alt="a&lt;b&gt;c" /></p>

Why this is the intended behaviour

Two independent references, both pointing the same way:

• JS parity. This project is a port of markdown-it and the changelog pins the parser to markdown-it v14.1.0. Upstream renderInlineAsText at that version handles text, image, html_inline, html_block, softbreak and hardbreak. The Python port is behind its own declared target for the last three.
• Internal consistency. softbreak and hardbreak are treated as an identical pair everywhere else in the codebase; 🐛 FIX: Newline not rendered in image alt attribute #157 previously added the softbreak branch to this very function but stopped there. This change is the sibling of that fix.

HTML content in alt is escaped downstream by renderAttrs → escapeHtml (so <b> becomes <b>), matching the JS behaviour — no markup reaches the attribute unescaped.

The fix

Two grouped branches added to renderInlineAsText, making it a 1:1 match of the upstream reference:

elif token.type in ("html_inline", "html_block"):
    result += token.content
elif token.type in ("softbreak", "hardbreak"):
    result += "\n"

Verification

• Added two cases to tests/test_port/fixtures/commonmark_extras.md (hard break and inline HTML in an image description), mirroring the existing 🐛 FIX: Newline not rendered in image alt attribute #157 soft-break fixture. Both fail without the change and pass with it.
• renderInlineAsText has a single production caller (the image renderer), and the soft-break / plain-text paths are unchanged (verified as controls).
• Full test suite: 983 passed. pre-commit ruff, ruff-format and mypy (strict) all clean.

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This PR was authored by an AI coding agent (Claude Code) running on this account: the AI found the bug, ran the repro, wrote the tests, and wrote this description. The human account holder reviews every change and is accountable for it. The verification above is real and re-runnable from the diff. If this isn't the kind of contribution you want, say so and I'll close it.